The functioning of a gas turbine engine depends on a continuous flow of a large volume of air through the components of the engine. Since these components, for example, the compressor rotor, are rotating at extremely high speeds any contaminants in the airflow will have a destructive effect on engine performance. Particles, such as super-cooled water droplets, impinging on the rotor may cause an imbalance and an eventual disintegration because of the high forces involved. It is, therefore, essential that some means be employed to separate contaminants from the airflow entering the engine plenum. In the past, a great variety of barrier filters were employed; however, these filters had the disadvantage of encouraging the formation of ice in the inlet which can eventually block the inlet and prevent the flow of air into the engine.
Inertial separator devices have been used to divide the particles of heavier mass in the inlet airflow away from the engine intake through a by-pass duct. A typical system of this type is described in U.S. Pat. No. 3,329,377 which issued on July 4, 1967. In this system a hinged deflecting vane is placed in the inlet duct upstream of the intake to the engine plenum. The vane extends into the duct restricting the airflow. The airflow is caused to accelerate and turn through a substantial angle around the deflecting vane. Particles of heavier mass cannot make the turn and are exhausted through a by-pass duct. The hinged nature of the vane allows the adjustment of the ratio of air by-passed. Since the deflecting vane is attached to the forward wall of the entrance to the engine plenum, it is always in the way of the airflow even at full retraction. This results in a pressure loss and prevents maximum ram air operation, resulting in an unnecessary limitation of engine performance.